The present invention relates to a magnetic disk unit and a magnetic head slider and, in particular, to a magnetic disk unit that flies the magnetic head slider above a magnetic disk for recording data and for the magnetic head slider for use in the unit.
A magnetic disk unit has a rotational magnetic disk, and a magnetic head slider which is mounted with a magnetic recording element and supported by a magnetic head support mechanism and positioned in a radial direction of the magnetic disk, and the unit is configured such that the magnetic head slider travels on the magnetic disk to record data into the magnetic disk. The magnetic head slider has an air lubrication bearing function and flies above a surface of the magnetic disk by a wedge film effect of air, so that the magnetic disk does not make solid contact directly with the magnetic head slider.
A magnetic head slider for use in a conventional magnetic disk unit includes a slider shown in JP-A-2002-25006 (patent literature 1), which is devised for preventing projection of the slider in a flying surface direction and breaking of a coil conductor itself due to heat generated by the coil conductor. The magnetic head slider has an inductive type, writing head element (magnetic recording element) including an upper core layer that is magnetically coupled to an upper magnetic pole at a front end, a lower core layer that is magnetically coupled to a lower magnetic pole at the front end, a coil conductor inserted between the upper core layer and the lower core layer, and a coil insulating layer formed with sandwiching the coil conductor. In the magnetic head slider shown in FIG. 7 of patent literature 1, a thermal diffusion member having a good heat transfer property is formed on the coil insulating layers in the outer rear and both lateral regions outside of the upper core layer, and a protective layer that is an insulating member is formed on the upper core layer and the thermal diffusion member.
Recently, in the magnetic disk unit, improvement in recording density and thus increase in capacity or decrease in size of the unit have been strongly desired. To realize these objectives, a distance between the magnetic head slider and the magnetic disk (or flying height of the slider) is effectively reduced to increase a line recording density of the magnetic disk.
Conventionally, in the design of the flying height of the slider, lowering of flying height due to variation in processing, difference in atmospheric pressure in use environment, and difference in temperature in use environment has been taken into account, and a flying height margin has been given such that the magnetic head slider does not contact the magnetic disk even in the worst condition.
There are two types of factors for the lowering of flying height due to the temperature difference in use environment. One of them is lowering of flying height due to local thermal-projection in a nanometer order caused by heated and thermally expanded neighborhood of a magnetic recording element of a magnetic head by generated heat. The heat is the sum of heat (iron loss) generated by eddy-current loss generated in a magnetic pole by electromagnetic induction when recording current flows through the coil conductor and heat (copper loss) generated in the coil conductor due to the recording current. Another is lowering of flying height due to local thermal-projection in a nanometer order caused by ambient-temperature rise because of the difference in linear expansion coefficients between a metal material of magnetic shield near the magnetic recording element or a magnetic pole and a ceramic insulating material of other portions.
Thus, if a slider that can keep a flying height responsive to the use environment can be realized, the flying height margin can be reduced, and while the magnetic head slider is prevented from contacting the magnetic disk, the flying height of the magnetic head slider can be significantly reduced.
Although heat generated by a writing head element is radiated into air from a surface of the protective layer through the thermal diffusion member and the protective layer in patent literature 1, since the heat radiation efficiency from the surface of the protective layer as the insulating member is low, and the surface area of the protective layer is small, the heat generated by the writing head element is hard to be radiated outside through the thermal diffusion member. Therefore, a problem that the thermal projection of a magnetic recording element part cannot be sufficiently suppressed, and the flying height margin cannot be sufficiently reduced, has remained.
When the thermal diffusion film is provided near the magnetic recording element as in patent literature 1, there has been a problem that when the ambient temperature rises, the thermal diffusion film also expands, whereby the thermal projection of the flying surface by the magnetic recording element is assisted.